1. Field of the Invention
The present invention relates to a thermal processor for processing a substrate such as a semiconductor wafer, a glass substrate for a liquid crystal display panel or a mask substrate for a semiconductor manufacturing apparatus by heating the same with a thermal processing plate.
2. Description of the Background Art
Such a thermal processor is employed for heating a photoresist film formed on the substrate before exposure (pre-baking), after exposure (post-exposure baking) or after development (post-baking) in a semiconductor manufacturing step, for example.
This thermal processor comprises a built-in thermal processing plate comprising heating means in a processing chamber for heating the substrate placed on the upper surface of the thermal processing plate. A spherical member is arranged on the thermal processing plate to slightly project from the upper surface thereof, for heating the substrate in a state proximately supporting the same with a small space referred to as a proximity gap.
Various photoresist materials are recently employed in response to the characteristics of patterns formed on substrates, and the thermal processor processes the substrates at various temperatures in correspondence thereto. Therefore, the temperature of the thermal processing plate provided on the thermal processor is preferably controllable to an arbitrary level.
In order to change the temperature of the thermal processing plate to a level higher than a preceding set temperature, the thermal processing plate may be rapidly heated with a heater. In order to change the temperature of the thermal processing plate to a level lower than the preceding set temperature, however, the thermal processing plate must inevitably be cooled by heat radiation. Therefore, a long time is required for changing the temperature of the thermal processing plate to a level lower than the preceding set temperature.
Thus, a plurality of thermal processors are set in a conventional substrate processor in response to the types of processing temperatures for substrates, thereby thermally processing the substrates by the thermal processors corresponding to the processing temperatures therefor. In this case, however, a large number of thermal processors must be set in the substrate processor, disadvantageously leading to increase of the occupation area and the setting cost thereof.
In order to solve this problem, a thermal processor provided with a cooling mechanism for cooling a thermal processing plate is proposed in general so that the temperature of the thermal processing plate can be quickly changed to a level lower than a preceding set temperature by rapidly forcibly cooling the thermal processing plate with the cooling mechanism.
When an air-cooling system feeding gas such as compressed air into a passage for a cooling fluid thereby performing cooling is employed as the cooling mechanism for such a conventional thermal processor, however, the heat exchange effectiveness is so inferior that the temperature of the thermal processing plate is reduced at an extremely slow speed even if the flow rate of the gas is increased.
Therefore, a water cooling system may be employed for using cooling water such as water in place of the compressed air and feeding the same into the passage for the cooling fluid thereby performing cooling. When the water cooling system is employed, however, the cooling water remaining in the passage for the cooling fluid is heated to a temperature exceeding the boiling point thereof to boil when heating the substrate. Therefore, the temperature of the thermal processing plate may be rendered ununiform or the thermal processing plate may be vibrated to exert bad influence on the result of processing the substrate. When the passage for the cooling fluid is brought into a closed structure isolated from the atmosphere and the cooling water boils in this passage, the pressure in the passage for the cooling fluid is abruptly increased, leading to a possibility of explosion or the like.
The present invention is directed to a thermal processor for heating a substrate with a thermal processing plate.
According to the present invention, the thermal processor heating a substrate comprises a thermal processing plate receiving the substrate thereon, a heating mechanism heating the thermal processing plate, a temperature reducing mechanism, reducing the temperature of the thermal processing plate, comprising a passage passing a cooling fluid therethrough, a coolant supply part supplying a cooling liquid to the passage and a gas supply part supplying gas to the passage, and a control part controlling the coolant supply part and the gas supply part to supply the gas to the passage after supplying the cooling liquid to the passage.
Cooling liquid is supplied to the passage for the cooling fluid, whereby the temperature of the thermal processing plate can be quickly reduced through the cooling liquid when performing temperature reduction control of the thermal processing plate. Further, the gas is supplied to the passage for the cooling fluid, whereby it is possible to prevent such a phenomenon that the cooling liquid remains in the passage and boils to exert bad influence on the result of processing the substrate.
According to a preferred mode of the present invention, the control part supplies the cooling liquid to the passage for reducing the temperature of the thermal processing plate and thereafter supplies the gas to the passage for reducing the temperature of the thermal processing plate at a speed lower than the speed for reducing the temperature with the cooling liquid.
Cooling liquid is supplied to the passage for reducing the temperature of the thermal processing plate at a high speed and thereafter the gas is supplied to the said passage for reducing the temperature of the thermal processing plate at a low speed, whereby the temperature of the thermal processing plate can be quickly set to a set level with no overshoot.
Accordingly, an object of the present invention is to provide a thermal processor capable of quickly reducing the temperature of a thermal processing plate to a set level without exerting bad influence on the result of processing a substrate.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.